In the manufacture of a three-dimensional article, it is common practice to first create a design of the article and then produce a prototype. After reviewing the initial design and prototype, design revisions are often made requiring the production of yet another prototype. This process of review and redesign may be repeated a number of times before finding the optimum design, thereby requiring that one or more prototypes be produced. Accordingly, the process of designing and prototyping an article may involve a considerable expense of time, effort and money.
Computer aided design (CAD) systems are commonly used for automating the design process. With the aid of a computer, an operator is able to design a three-dimensional article and display the design on a two-dimensional medium such as a display screen or paper. The computer aids in the design as called for by the operator according to pre-existing design parameters and computer software.
Computer aided milling machines for milling articles in response to computer generated signals are also commonly used to make certain articles. In these machines, a computer generated data file representative of the article to be produced is used to control the operation of the machine. Milling tools within the machine shape a body of material. Relatively coarse tools may be used to shape coarse features of the article, while finer tools may be used to finish the article. These machines, however, are relatively large, expensive and limited in the article geometries that may be produced.
Accordingly, systems have been developed wherein a three-dimensional article is constructed in successive layers based upon three-dimensional CAD data. For example, stereolithography has been one approach to the problem of producing a prototype of an article layer by layer. An example of stereolithography is disclosed in U.S. Pat. No. 4,575,330 to Hull entitled "Apparatus for Production of Three-Dimensional Objects By Stereolithography." Hull discloses an apparatus whereby articles are produced by forming successive, adjacent, cross-sectional laminae of the article at the surface of a fluid medium. The fluid medium is capable of altering its physical state from a fluid to a solid in response to stimulation, such as by UV radiation; particle bombardment, such as electron beams; chemical reaction; or impinging radiation other than UV radiation. The apparatus includes a source of stimulation which may be selectively applied to the surface of the fluid medium to produce the cross-sectional laminae of the article. The source of selective stimulation is controlled by a computer in response to coordinate data.
Stereolithography, however, requires the use of more material than is actually incorporated in the article being produced, and also requires the exact placement of the article being constructed relative to the surface of the fluid medium. In addition, the depth of the layer created when the fluid surface is exposed to the stimulation may be difficult to control.
An apparatus and method for forming three-dimensional articles from a material which is normally solid but flowable when heated is disclosed in U.S. Pat. No. 5,141,680 to Almquist et al. entitled "Thermal Stereolithography." This patent discloses a conventional stereolithography apparatus employing a container of material capable of physical transformation from a fluid to a solid upon exposure to synergistic stimulation. The patent also discloses recoating means including a doctor blade to rapidly coat fresh layers of resin prior to exposing the layer to the synergistic stimulation.
Another modeling system including a moveable table positioned in a photohardenable substance, and including a doctor knife for periodic vertical leveling is disclosed in U.S. Pat. No. 5,128,235 to Vassiliou et al. entitled "Method of Forming a Three-Dimensional Object Comprising Additives Imparting Reduction of Shrinkage To Photohardenable Compositions."
U.S. Pat. No. 5,260,009 to Penn entitled "System, Method, and Process for Making Three-Dimensional Objects" discloses a system wherein an object is formed in successive layers. A positive material is dispensed in layers to form the object, and a mold material is dispensed around each layer of positive material to provide support. A cutting device is arranged to plane the uppermost surface of the positive material to expose the positive material and to compensate for surface height variations.
U.S. Pat. No. 5,126,529 to Weiss et al. entitled "Method and Apparatus for Fabrication of Three-Dimensional Articles by Thermal Spray Deposition" discloses a system wherein a milling or grinding tool is used to assure that a uniform, constant and repeatable thickness of material is deposited each layer.
A modeling system including an extrusion head is disclosed in U.S. Pat. No. 4,749,347 to Valavaara entitled "Topology Fabrication Apparatus." This patent discloses a system that progressively extrudes and deposits portions of a three-dimensional solid body. This patent also discloses a gate or doctor blade that may be tilted to define the angle of slope along the upper edge of the extruded strip. Similarly U.S. Pat. No. 5,121,329 to Crump entitled "Apparatus and Method for Creating Three-Dimensional Objects" discloses an apparatus wherein a flow of material through a nozzle is used to create a three-dimensional object. The bottom flat face of the nozzle provides a doctor blade effect as the nozzle and substrate are moved relative to one another. By surface contact with the layer of material as it is being dispensed, the dispenser tip limits the top of each layer to the precise vertical or z-axis setting, and thus assists in regulating the thickness of each layer to reduce accumulated error along the z-axis.
A major advance in the art of three-dimensional modeling is disclosed in U.S. Pat. No. 4,665,492 to Masters entitled "Computer Automated Manufacturing Process and System." This patent discloses an apparatus including: an ejection head having an ejection nozzle for emitting small mass particles or droplets of particulate matter; a servo-mechanism for manipulating the ejection head and nozzle; and a machine controller for controlling the servo-mechanism in response to a data file containing coordinate information representing the design of the article being produced. The mass particles are directed to the precise coordinates of a three-dimensional article as defined by the computer data file. The mass particles may include plastic material, a slurry material having water content, and charged particles which are electrically deflected. The disclosure of Masters, however, does not directly address the problem of reducing uneven surface portions resulting from a possible accumulation of small uneven portions in each layer of particles.
Other U.S. patents related to three-dimensional modeling are listed as follows: U.S. Pat. No. 5,257,657 to Gore; U.S. Pat. No. 5,136,515 to Helinski; U.S. Pat. No. 5,059,266 to Yamane et al.; U.S. Pat. No. 5,140,937 to Yamane et al.; U.S. Pat. No. 5,149,548 to Yamane et al.; U.S. Pat. No. 5,207,371 to Prinz et al.; U.S. Pat. No. 5,301,415 to Prinz et al.; U.S. Pat. No. 5,301,863 to Prinz et al.; U.S. Pat. No. 5,204,124 to Secretan et al.; U.S. Pat. No. 5,303,141 to Batchelder et al.; U.S. Pat. No. 5,031,120 to Pomerantz et al.; and U.S. Pat. No. 5,287,435 to Cohen et al.